fix(resolve): Warn on Self-Type Lifetime Elision for Non-`Self` Types by TKanX · Pull Request #153692 · rust-lang/rust

TKanX · 2026-03-11T05:27:05Z

Summary

FCW lint self_lifetime_elision_not_applicable: fires when a self parameter contains & but does not syntactically contain Self.

Tracking: #140611

Context

Self-type lifetime elision in rustc_resolve relies on a name-matching hack (is_self_ty) that shallow-compares Res values between the self parameter type and the impl self type. As @compiler-errors identified in #140611, this hack cannot see through type aliases (different Res) and only fires for Struct|Union|Enum|PrimTy impls (excludes TyAlias). When it misses, find_lifetime_for_self returns Empty, self-elision silently fails, and a later parameter's lifetime may leak into the return type.

@lcnr proposed restricting self-elision to genuine Self and FCW'ing everything else. This PR implements that.

Behavior

pub struct W<'a>(&'a ());
pub type Alias<'a> = W<'a>;

Case	Code	Before	After
f1	`impl Alias { fn f(self: &W) -> &() }`	silent wrong `'_`	FCW
f2	`impl Alias { fn f(self: &Alias) -> &() }`	silent wrong `'_`	FCW
f3	`impl Alias { fn f(&self) -> &() }`	correct	unchanged
f4	`impl W { fn f(self: &W) -> &() }`	correct (hack fires)	FCW
f5	`impl W { fn f(self: &Alias) -> &() }`	silent wrong `'_`	FCW
f6	`impl W { fn f(&self) -> &() }`	correct	unchanged

A follow-up PR will remove the hack after a warning period.

r? @lcnr
cc @compiler-errors @traviscross

rustbot · 2026-03-11T09:50:04Z

Some changes occurred in compiler/rustc_hir/src/attrs

cc @jdonszelmann, @JonathanBrouwer

lcnr · 2026-03-12T11:28:42Z

before discussing this in a lang meeting, can you extend the PR description a bit to summarize the reasoning and discussion behind this?

Co-authored-by: lcnr <rust@lcnr.de> Co-authored-by: Michael Goulet <michael@errs.io>

…ting tests

…dicate`

…e-match, r=<try> fix(resolve): Warn on Self-Type Lifetime Elision for Non-`Self` Types

rust-bors · 2026-03-18T19:59:42Z

💔 Test for b9f802f failed: CI

rustbot · 2026-03-18T20:02:55Z

Reminder, once the PR becomes ready for a review, use @rustbot ready.

…deny for crater run (WILL BE REVERTED) Co-authored-by: Travis Cross <tc@traviscross.com>

rust-bors · 2026-03-19T01:21:51Z

@TKanX: 🔑 Insufficient privileges: not in try users

traviscross · 2026-03-19T02:01:17Z

@bors try

…e-match, r=<try> fix(resolve): Warn on Self-Type Lifetime Elision for Non-`Self` Types

rust-bors · 2026-03-19T04:12:12Z

☀️ Try build successful (CI)
Build commit: 3960581 (39605810efb1a0d52f955bfba9e4eec7a01d5deb, parent: fd0c901b00ee1e08a250039cdb90258603497e20)

traviscross · 2026-03-19T04:28:56Z

@craterbot check

craterbot · 2026-03-19T04:29:22Z

👌 Experiment pr-153692 created and queued.
🤖 Automatically detected try build 3960581
🔍 You can check out the queue and this experiment's details.

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

rust-bors · 2026-03-20T11:14:15Z

☔ The latest upstream changes (presumably #154123) made this pull request unmergeable. Please resolve the merge conflicts.

craterbot · 2026-03-24T14:16:32Z

🚧 Experiment pr-153692 is now running

ℹ️ Crater is a tool to run experiments across parts of the Rust ecosystem. Learn more

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Mar 11, 2026

TKanX force-pushed the bugfix/140611-self-lifetime-elision-name-match branch from 7f7909c to 9922812 Compare March 11, 2026 05:35

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TKanX force-pushed the bugfix/140611-self-lifetime-elision-name-match branch from ea23a3d to 7e85048 Compare March 11, 2026 07:18

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TKanX force-pushed the bugfix/140611-self-lifetime-elision-name-match branch from 7e85048 to 7a90db6 Compare March 11, 2026 08:14

rustbot assigned lcnr Mar 11, 2026

TKanX marked this pull request as ready for review March 11, 2026 09:50

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Mar 11, 2026

rustbot removed the S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. label Mar 11, 2026

TKanX marked this pull request as draft March 12, 2026 19:02

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 12, 2026

fix(resolve): Warn on self-type lifetime elision for non-Self types

3982f64

Co-authored-by: lcnr <rust@lcnr.de> Co-authored-by: Michael Goulet <michael@errs.io>

TKanX force-pushed the bugfix/140611-self-lifetime-elision-name-match branch 2 times, most recently from f6ec003 to dfcd644 Compare March 12, 2026 20:23

TKanX added 2 commits March 12, 2026 13:38

test(resolve): Allow self_lifetime_elision_not_applicable in pre-exis…

08525dd

…ting tests

fix(hir): Heed our own lint in `OnUnimplementedCondition::matches_pre…

805f449

…dicate`

TKanX force-pushed the bugfix/140611-self-lifetime-elision-name-match branch from dfcd644 to 805f449 Compare March 12, 2026 20:38

TKanX marked this pull request as ready for review March 12, 2026 20:39

rustbot added the S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. label Mar 12, 2026

rust-bors bot pushed a commit that referenced this pull request Mar 18, 2026

Auto merge of #153692 - TKanX:bugfix/140611-self-lifetime-elision-nam…

b9f802f

…e-match, r=<try> fix(resolve): Warn on Self-Type Lifetime Elision for Non-`Self` Types

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rust-bors bot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 18, 2026

TKanX force-pushed the bugfix/140611-self-lifetime-elision-name-match branch from 52625a2 to 5d87eb2 Compare March 18, 2026 20:18

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TKanX force-pushed the bugfix/140611-self-lifetime-elision-name-match branch from 347424a to ddda958 Compare March 18, 2026 22:50

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test(lint): Temporarily bump self_lifetime_elision_not_applicable to …

e46d6c7

…deny for crater run (WILL BE REVERTED) Co-authored-by: Travis Cross <tc@traviscross.com>

TKanX force-pushed the bugfix/140611-self-lifetime-elision-name-match branch from ddda958 to e46d6c7 Compare March 18, 2026 23:35

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rustbot added S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Mar 19, 2026

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rust-bors bot pushed a commit that referenced this pull request Mar 19, 2026

Auto merge of #153692 - TKanX:bugfix/140611-self-lifetime-elision-nam…

3960581

…e-match, r=<try> fix(resolve): Warn on Self-Type Lifetime Elision for Non-`Self` Types

craterbot added S-waiting-on-crater Status: Waiting on a crater run to be completed. and removed S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. labels Mar 19, 2026

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TKanX commented Mar 11, 2026 •

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